Our long-term goal is to understand the mechanisms that are responsible for resistance to apoptosis in prostate cancer. Understanding the mechanisms involved in apoptosis in a slowly proliferating cancer such as prostate cancer is critical. The studies proposed focus on TRAIL, which plays a critical role in apoptosis in many different cell types, and are designed to understand the mechanisms of TRAIL-induced apoptosis in human prostate cancer. In preliminary studies, we have determined that prostatic carcinoma cell lines respond differently to TRAIL (only a subset are sensitive), and that resistance is dominant. In addition, we provide evidence that the mitochondrial pathway is involved in TRAIL-induced cell death and that there is an unusual caspase activation cascade, particularly in resistant cells suggesting a possible mechanism of resistance. Finally, we have determined that several kinase pathways are involved in modulating the signal transduction pathways, particularly the PI3K/Akt and NF-kB cascades. The proposed studies will provide a mechanistic understanding of TRAIL induced apoptosis in prostatic epithelial cells and addresses fundamental issues raised in the NCI's recent report on prostate cancer. We believe that the signaling transduction pathways which have been minimally elucidated in other cells systems, principally lymphoid cells, are different in (benign and) malignant epithelial cells, such as those of prostatic origin. We hypothesize that distinct signaling pathways confer resistance of prostatic carcinoma cells to TRAIL-induced programmed cell death. To test our hypothesis and identify the mechanisms that are responsible for TRAIL-mediated apoptosis in prostate cancer, we propose the following Specific Aims: Aim 1: Determine the adapter and signaling molecules that are required for TRAIL-induced caspase activation; Aim 2. Determine the role of the mitochondrial pathway in TRAIL-induced apoptosis: Aim 2A. Determine the role of mitochondrial-localized apoptogenic factors; Aim 2B. Determine the mitochondrial-related caspase(s) that is involved in the processing of caspase-3; Aim 3: Determine the role of the PI3K/Akt and NF-kB pathways in TRAIL-induced apoptosis; Aim 4: Determine the effects of TRAIL and TRAIL receptor expression on human prostatic epithelial cells.